The present invention relates to a double-end surface grinding machine designed to feed a work between a pair of grinding wheels driven rotationally and to grind opposite surfaces of the work simultaneously with the two wheels.
A known double-end surface grinding machine is provided on a main frame with a pair of coaxially opposing sleeves which are axially movable by means of a suitable driving device via worms or the like, spindles driven rotationally by a motor through a belt transmitting device and being respectively supported freely rotationally within the sleeves, wheels mounted respectively on the adjoining ends of the spindles, with grinding surfaces opposing each other, and a carrier plate mounted on a carrier frame formed integrally on the front side of the main frame, and rotatable in a plane normal to the wheel axis in such a manner that its peripheral edge overlaps between the wheels, thereby to feed the work therebetween by the carrier plate to grind the opposite surfaces of the work simultaneously with the two wheels.
In the double-end surface grinding machine described above, replacement and dressing of the wheels, cleaning and maintenances of the machine may be performed entirely through windows opened on both sides of the main frame. However, since the windows provided on the sides of the main frame are generally smaller, there is such a disadvantage as that a working space would be limited. Thus, for example, when replacing the wheel which weighs about 50 to 80 kg, the limited working space through the window enforces a very dangerous work which was time consuming at the same time and resulted in a poor efficiency.
When grinding the work with the double-end surface grinding machine mentioned above, upper and lower edges of the work must be projected from both surfaces of the carrier plate by forming the thickness of the carrier plate thinner than that of the work, and in order to grind the work precisely in this state, it is desirable to make the upper and lower projections of the work even. Thus, when the thickness of the work is changed, its projection must be adjusted to become even. In the past, in such case, a spacer for adjusting the projection was interposed between the carrier plate and a mounting board onto which the carrier plate is mounted, and replaced to adjust the upper and lower projections of the work. However, since the carrier plate must be removed from the mounting board to replace the spacer, replacement is extremely complicated and annoying.
In some of the double-end surface grinding machines, a rotating motion is given to the work to improve its grinding efficiency. That is, on the carrier frame, in place of the carrier plate, a swivel arm oscillating and swinging within a range of prescribed angle in a plane normal to the wheel axis, is disposed in such a manner that is periphery overlaps partially between the wheels, on the swivel arm a work pocket gear retaining the work eccentrically is supported freely rotationally, said work pocket gear being coupled via suitable transmitting means to a driving motor, which rotates the work pocket gear to provide the rotating motion to the work. In this case, if the thickness of the work being ground is thinner, the thickness of the swivel arm becomes thinner accordingly and the work pocket gear can be hardly supported through a bearing or the like from the dimensional point of view. Therefore, the work pocket gear is supported by a rotating support provided at one portion thereof and placed on the swivel arm. However, since the work pocket gear makes a sliding rotation with respect to the swivel arm, a contact between the work pocket gear and swivel arm tends to wear soon. In particular, wheel powders, grinding chips or the like entering the contact between the work pocket gear and swivel arm at grinding accelerate such wear. As the wear grows larger, a jolt of the contact increases to deteriorate the interlocking of gears, thereby the rotation becomes irregular or stops to cause a poor grinding accuracy. Therefore, a hardened steel or a hard metal are used for the contact hitherto, which is so far ineffective.
In the double-end surface grinding machine, in order to provide a cutting allowance to the work, a grinding condition is set to tilt the axis of the upper wheel with respect to that of the lower wheel to bring the distance between the grinding surfaces of the wheels in such a manner that, the take out position of the work is narrower than the feeding position by the cutting allowance. As means to tilt the axis of upper wheel relative to that of the lower wheel in such a way, in the past, the main frame is divided into upper and lower portions, whereby the upper portion supporting an upper quill if the upper wheel is brought to tilt optionally with respect to the lower portion supporting a lower quill of the lower wheel to enable the upper wheel axis to tilt optionally relative to the lower wheel axis, but the tilting of the upper portion is extremely troublesome and time consuming. Besides,. since the upper wheel axis is tilted by tilting the upper frame, the main frame must be divided, thus strength of the main frame is deteriorated. Accordingly, when the moment is resisted by the frame due to a grinding reaction force applied on the wheels by the grinding resistance, the grinding surfaces of the wheel tend to tilt during grinding, so that the dimensional tolerances can not be maintained accurately for the precise machining.
Now, in the-double-end surface grinding machine, if the wheels are used for a long period of time or its grinding condition is inadequate, the grinding surfaces of the wheels are crushed and stuffed to deteriorate the grinding performance and to raise the heat value, thereby causing cracks and fusions on the finished surfaces.
Therefore, when the grinding surfaces of the wheels are crushed or stuffed, worn particles on the upper layer of grinding surfaces and chips stuffed between such particles or pores must be removed, and the grinding surfaces must be dressed to expose new particles thereon.
Normally a dresser is utilized for dressing. The dresser is formed by projecting diamond tools on the upper and lower tips of a dress-arm which is disposed on the main frame so as to be driven swingingly within a plane normal to the wheel axis by a dress-arm driving motor, by driving the dress arm swingingly and inserting the diamond tools between the rotating wheels to move radially of the wheels, worn grinding particles on the upper layer of the grinding surfaces or stuffed chips on the wheels are shaved off, and the new grinding particles may be exposed on the grinding surfaces of the wheels.
In dressing using the dresser, since revolution of the wheels is constant, different circumferential speeds occur on the grinding surfaces of the wheels, thus the collision speeds between the grinding particles of the wheels and the diamond tools of the dresser differ from each other causing uneven dressing of the entire grinding surfaces and insufficient accuracy regardless of the dressing. For example, the shape which is otherwise a plane normal to the wheel axis after the dressing, becomes inclined against the plane normal to the wheel axis. This is because, as the diamond tools proceed diametrically inside the grinding surfaces, the grinding particles of the wheels are shaved off more than necessary by the dressing resistance applied thereon, since the circumferential speed of the grinding surfaces of the wheels is slow.